Corrosion resistant solar mirror

ABSTRACT

A reflective article includes a transparent substrate having a first major surface and a second major surface. A base coat is formed over at least a portion of the second major surface. A primary reflective coating having at least one metallic layer is formed over at least a portion of the base coat. A protective coating is formed over at least a portion of the primary reflective coating. The article further includes a solar cell and an anode, with the solar cell connected to the metallic layer and the anode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to and claims the benefits of U.S.application Ser. Nos. 12/330,580; 12/330,618; and 12/330,651, all filedon Dec. 9, 2008 and all of which are herein incorporated by reference.

NOTICE OF GOVERNMENT SUPPORT

This invention was made with Government support under GovernmentContract No. DE-FC36-08G018033 (DOE Solar Power) awarded by the U.S.Department of Energy. The United States Government may have certainrights in this invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to solar mirrors and, in one particularembodiment, to a solar mirror having improved anticorrosion propertiesfor the metallic layer of the mirror.

2. Technical Considerations

With the increasing costs of fossil-based fuels, solar power is becominga more commercially acceptable and economically viable source of energy.One known application is using mirrors to concentrate solar power forelectrical generation. Mirrors having high reflectance of solarradiation are used for “concentrated solar thermal power” (CSTP)installations. One conventional system uses curved parabolic solarmirrors to concentrate solar energy onto tubes positioned along a focalline. A heat transfer medium in the tubes carries the absorbed heatenergy to a generator station where it is used for power generation.Another conventional system uses a solar tower in which a number of flatsolar mirrors direct solar energy at a particular location on the tower.The heat generated by the focused solar energy is transferred to aworking fluid, such as sodium, and the heated working fluid is used forpower generation. A further application of such mirrors is for“concentrated photovoltaics” (CPV). In this application, mirrors focusor concentrate solar energy onto high-efficiency photovoltaic (PV)devices, thereby improving the energy output per device.

In these systems, it is desirable that the mirrors reflect as much solarenergy as possible. It is also desirable that the mirrors have as long acommercial life as possible to preclude frequent changing of themirrors.

Conventional solar mirrors utilize a reflective metal layer to reflectthe solar energy. These mirrors are positioned outdoors in an array thatcan include hundreds or thousands of mirrors. Since the mirrors areexposed to environmental conditions, such as rain, snow, airbornecontaminants, etc., a problem with these conventional solar mirrors isthat the reflective metal layer can become corroded or degraded byattack from moisture or airborne contaminants. Some solar mirrorsinclude a casing or backing to help keep out such materials. However,with age and wear, the backings can crack or break, allowing moisture toenter and corrode the metal layer. This corrosion decreases thereflectance of the mirror and shortens the commercial life of themirror.

Therefore, it would be advantageous to provide a reflective article,such as a solar mirror, with increased resistance to corrosion.

SUMMARY OF THE INVENTION

A reflective article comprises a substrate having a first major surfaceand a second major surface. A primary reflective coating comprising atleast one metallic layer is formed over at least a portion of a majorsurface of the substrate. An anode, such as a sacrificial anode, is inelectrical contact with the metallic layer of the primary reflectivecoating. The anode can comprise a material having a greater oxidationpotential than the metallic layer.

A further reflective article comprises a substrate having a first majorsurface and a second major surface. A primary reflective coatingcomprising at least one metallic layer is formed over at least a portionof a major surface of the substrate. A source of electrons, such as abattery, solar cell, or similar source of electrical potential, is inelectrical contact with the metallic layer of the primary reflectivecoating.

Another reflective article comprises a transparent substrate having afirst major surface and a second major surface. A base coat is formedover at least a portion of the second major surface. A primaryreflective coating comprising at least one metallic layer is formed overat least a portion of the base coat. A protective coating is formed overat least a portion of the primary reflective coating. The articlefurther comprises a source of electrons, such as a solar cell and/or abattery, and an anode, with the source of electrons connected to themetallic layer and the anode.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the following drawingfigures wherein like reference numbers identify like parts throughout.

FIG. 1A is a side, sectional view (not to scale) of a reflective articleincorporating features of the invention;

FIG. 1B is a side, sectional view (not to scale) of another reflectivearticle incorporating features of the invention;

FIG. 1C is a side, sectional view (not to scale) of a further reflectivearticle incorporating features of the invention;

FIG. 2 is a side, sectional view (not to scale) of another reflectivearticle of the invention;

FIG. 3 is a side, sectional view (not to scale) of a further reflectivearticle of the invention;

FIG. 4 is a side, sectional view (not to scale) of an additionalreflective article of the invention;

FIG. 5 is a side view (not to scale) of a reflective article of theinvention attached to a base;

FIG. 6 is a side view (not to scale) of a reflective article having apassive corrosion reducing assembly;

FIG. 7 is a schematic view of an active corrosion reducing assembly fora reflective article;

FIG. 8 is a front view (not to scale) of a reflective articleincorporating an active corrosion assembly; and

FIG. 9 is a side, sectional view (not to scale) of the reflectivearticle of FIG. 8 taken along the line IX-IX of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used herein, spatial or directional terms, such as “left”, “right”,“inner”, “outer”, “above”, “below”, and the like, relate to theinvention as it is shown in the drawing figures. However, it is to beunderstood that the invention can assume various alternativeorientations and, accordingly, such terms are not to be considered aslimiting. Further, as used herein, all numbers expressing dimensions,physical characteristics, processing parameters, quantities ofingredients, reaction conditions, and the like, used in thespecification and claims are to be understood as being modified in allinstances by the term “about”. Accordingly, unless indicated to thecontrary, the numerical values set forth in the following specificationand claims may vary depending upon the desired properties sought to beobtained by the present invention. At the very least, and not as anattempt to limit the application of the doctrine of equivalents to thescope of the claims, each numerical value should at least be construedin light of the number of reported significant digits and by applyingordinary rounding techniques. Moreover, all ranges disclosed herein areto be understood to encompass the beginning and ending range values andany and all subranges subsumed therein. For example, a stated range of“1 to 10” should be considered to include any and all subranges between(and inclusive of) the minimum value of 1 and the maximum value of 10;that is, all subranges beginning with a minimum value of 1 or more andending with a maximum value of 10 or less, e.g., 1 to 3.3, 4.7 to 7.5,5.5 to 10, and the like. Further, as used herein, the terms “formedover”, “deposited over”, or “provided over” mean formed, deposited, orprovided on but not necessarily in direct contact with the surface. Forexample, a coating layer “formed over” a substrate does not preclude thepresence of one or more other coating layers or films of the same ordifferent composition located between the formed coating layer and thesubstrate. As used herein, the terms “polymer” or “polymeric” includeoligomers, homopolymers, copolymers, and terpolymers, e.g., polymersformed from two or more types of monomers or polymers. The terms“visible region” or “visible light” refer to electromagnetic radiationhaving a wavelength in the range of 380 nm to 780 nm. The terms“infrared region” or “infrared radiation” refer to electromagneticradiation having a wavelength in the range of greater than 780 nm to100,000 nm. The terms “ultraviolet region” or “ultraviolet radiation”mean electromagnetic energy having a wavelength in the range of 100 nmto less than 380 nm. Additionally, all documents, such as but notlimited to issued patents and patent applications, referred to hereinare to be considered to be “incorporated by reference” in theirentirety. Also, parameters such as “visible transmission” and “visiblereflection” and the like are those determined using conventionalmethods. Those skilled in the art will understand that properties suchas visible transmission or visible reflection can vary based on thephysical dimensions, e.g., thickness, of the article being tested.Therefore, any comparison to the present invention should be calculatedat an equivalent thickness.

For purposes of the following discussion, the invention will bediscussed with reference to use with a reflective article to reflectelectromagnetic radiation, such as but not limited to a solar mirror toreflect electromagnetic solar radiation. As used herein, the term “solarmirror” refers to any article configured to reflect electromagneticsolar radiation, such as visible and/or infrared and/or ultravioletradiation, e.g., for use in concentrated solar power systems. However,it is to be understood that the invention is not limited to use withsolar mirrors but could be practiced with articles in other fields, suchas but not limited to laminated or non-laminated residential and/orcommercial mirrors, or reflectors for high-performance optical systems(e.g., video projectors or optical scanners), just to name a few.Therefore, it is to be understood that the specifically disclosedexemplary embodiments are presented simply to explain the generalconcepts of the invention and that the invention is not limited to thesespecific exemplary embodiments.

In one aspect, the reflective article of the invention comprises atleast some of the following components: (1) a light-transmittingsubstrate or superstrate having low absorption of solar radiation in theregion(s) of the electromagnetic spectrum that it is desirable for thearticle to reflect, (2) one or more primary reflective layer(s) havinghigh reflectivity of solar radiation in the region(s) of theelectromagnetic spectrum that is desirable to be reflected, (3) optional“primer” or “blocker” or “barrier” layer(s) which can help preserve thereflective properties of the reflective layer(s) and/or improve theadhesion of adjacent components, (4) one or more optional secondaryreflective layers such as additional metal, semiconductor, dielectric,and/or composite layers which can enhance the reflectivity of thearticle over some or all of the desired wavelength range and/or serve toprotect the primary reflective layer(s) and/or serve to preventdiffusion of chemical species between layers and/orsubstrates/superstrates, (5) optional corrosion-inhibiting layer(s), (6)optional sacrificial layer(s) comprising materials which exhibit greaterpropensity to corrode than the materials comprising components 2, 3,and/or 4, (7) optional layer(s) of materials (e.g. metal or metalalloys) which are corrosion-resistant and/or form passivation layersthat prevent chemically-reactive environmental species frominteracting/reacting with other components, (8) optional encapsulationlayer(s) which protect underlying layers (especially reflectivelayer(s)) from attack by environmental hazards (e.g. atmosphericpollutants, water, mechanical hazards), (9) optional adhesive layer(s)which bond the article to optional underlyinglamina/plies/substrates/superstrates or other supporting structures,(10) optional polymeric layer(s), (11) optional additionallamina/plies/substrates/superstrates, (12) optional low-maintenance(e.g. hydrophillic and/or photocatalytic or hydrophobic) top surface,and (13) optional edge sealants.

A non-limiting reflective article incorporating features of theinvention is illustrated in FIG. 1A and will be described herein as asolar mirror 1. The solar mirror 1 can have any desired reflectance ortransmittance in the region(s) of interest within the electromagneticspectrum (e.g., ultraviolet, visible, near infrared, far infrared,microwave, radiowave, etc.). For example, the solar mirror 1 can have avisible light reflection at a wavelength of 550 nm of at least 85%, suchas at least 90%, such as at least 95%.

In the embodiment illustrated in FIG. 1A, the solar mirror 1 includes asubstrate or ply 12 with a first major surface 14, i.e. an outer majorsurface, and an opposed second major surface 16, i.e. an inner majorsurface. In the following discussion, the first major surface 14 facesthe incident radiation and the second surface 16 faces opposite thedirection of the incident radiation. An optional basecoat 102 can beprovided over at least a portion of one of the major surfaces, such asthe second major surface 16. In illustrated non-limiting embodiment, aprimary reflective coating 22 is formed over at least a portion of thesecond major surface 16, e.g. over at least a portion of the basecoat102, if present. A protective coating 50 is provided over at least aportion of the primary reflective coating 22. While in the illustratedembodiment the coatings are formed over the second major surface 16, itis understood that at least some of the coatings could alternatively beformed over the first major surface 14.

In the broad practice of the invention, the ply 12 can include anydesired material having any desired characteristics. For example, theply 12 can be transparent or translucent to visible light. By“transparent” is meant having a transmission of greater than 0% up to100% in a desired wavelength range, such as visible light.Alternatively, the ply 12 can be translucent. By “translucent” is meantallowing electromagnetic radiation (e.g., visible light) to betransmitted but diffusing or scattering this radiation. Examples ofsuitable materials for the ply 12 include, but are not limited to,thermoplastic, thermoset, or elastomeric polymeric materials, glasses,ceramics, and metals or metal alloys, and combinations, composites, ormixtures thereof. Specific examples of suitable materials include, butare not limited to, plastic substrates (such as acrylic polymers, suchas polyacrylates; polyalkylmethacrylates, such aspolymethylmethacrylates, polyethylmethacrylates,polypropylmethacrylates, and the like; polyurethanes; polycarbonates;polyalkylterephthalates, such as polyethyleneterephthalate (PET),polypropyleneterephthalates, polybutyleneterephthalates, and the like;polysiloxane-containing polymers; or copolymers of any monomers forpreparing these, or any mixtures thereof); ceramic substrates; glasssubstrates; or mixtures or combinations of any of the above. Forexample, the ply 12 can include conventional soda-lime-silicate glass,borosilicate glass, or leaded glass. The glass can be clear glass. By“clear glass” is meant non-tinted or non-colored glass. Alternatively,the glass can be tinted or otherwise colored glass. The glass can beannealed or heat-treated glass. As used herein, the term “heat treated”means tempered, bent, heat strengthened, or laminated. The glass can beof any type, such as conventional float glass, and can be of anycomposition having any optical properties, e.g., any value of visibletransmission, ultraviolet transmission, infrared transmission, and/ortotal solar energy transmission. The ply 12 can be, for example, clearfloat glass or can be tinted or colored glass. Although not limiting tothe invention, examples of glass suitable for the ply 12 are describedin U.S. Pat. Nos. 4,746,347; 4,792,536; 5,030,593; 5,030,594; 5,240,886;5,385,872; and 5,393,593. The ply 12 can be of any desired dimensions,e.g., length, width, shape, or thickness. In one exemplary embodiment,the first ply 12 can be greater than 0 up to 10 mm thick, such as 1 mmto 10 mm thick, e.g., 1 mm to 5 mm thick, e.g., less than 4 mm thick,e.g., 3 mm to 3.5 mm thick, e.g., 3.2 mm thick. Additionally, the ply 12can be of any desired shape, such as flat, curved, parabolic-shaped, orthe like. Also, when the primary reflective layer(s) 22 reside on thesecond major surface 16 of the article, the ply 12 can comprise one ormore materials that exhibit low absorption of electromagnetic radiationin the region(s) of electromagnetic radiation desired to be reflected.

In one non-limiting embodiment, the ply 12 can have a high visible lighttransmission at a reference wavelength of 550 nanometers (nm) and areference thickness of 3.2 mm. By “high visible light transmission” ismeant visible light transmission at 550 nm of greater than or equal to85%, such as greater than or equal to 87%, such as greater than or equalto 90%, such as greater than or equal to 91%, such as greater than orequal to 92%, such as greater than or equal to 93%, such as greater thanor equal to 95%, at 3.2 mm reference thickness for the ply. Particularlyuseful glass for the practice of the invention is disclosed in U.S. Pat.Nos. 5,030,593 and 5,030,594. Non-limiting examples of glass that can beused for the practice of the invention include, but are not limited to,Starphire®, Solarphire®, Solarphire® PV, Solargreen®, Solextra®, GL-20®,GL-35™, Solarbronze®, CLEAR, and Solargray® glass, all commerciallyavailable from PPG Industries Inc. of Pittsburgh, Pa.

The basecoat 102 can provide a stronger or more durable interfacebetween the ply 12 and the primary reflective coating 22. The basecoat102 can comprise one or more materials chosen such that the interfacebetween the basecoat 102 and the primary reflective coating 22 is moremechanically, chemically, and/or environmentally stable than aninterface between the ply 12 and the primary reflective layer 22. Also,the basecoat 102 can serve as a diffusion barrier to the elementalexchange between the ply 12 and the primary reflective coating 22 (suchas the migration of sodium out of the glass substrate into the overlyingcoating(s) or the migration of metal, e.g., silver, from the primaryreflective coating 22 to the glass), especially as might occur as theresult of subjecting the coated article to elevated temperatures, forexample, for bending or heat strengthening. Additionally oralternatively, the basecoat 102 can provide a smoother or more planarsurface upon which to deposit an overlaying coating, e.g., the primaryreflective coating 22. Examples of materials suitable for the basecoat102 include, but are not limited to, inorganic materials such as but notlimited to transparent low absorption dielectrics, such as metal oxidesor combinations, composites, or mixtures of metal oxides. Examples ofsuitable metal oxides include alumina, titania, zirconia, zinc oxide,zinc stannate, tin oxide, or mixtures or combinations thereof. Otherexamples for the basecoat 102 include one or more layers of silicondioxide and/or silicon nitride. In one non-limiting embodiment, thebasecoat 102 comprises titania. The basecoat 102 can have anycomposition or thickness to provide sufficient functionality to thearticle (e.g., mechanical, chemical, passivation, planarization,adhesion, diffusion barrier properties, environmental durabilityenhancement, optical, and the like). In one particular embodiment wherethe basecoat 102 is titania, the basecoat 102 has a thickness in therange of 0.1 nm to 5 nm, such as 0.1 nm to 3 nm, such as 0.5 nm to 3 nm,such as 1 nm to 3 nm, such as 0.5 nm to 2 nm, such as 1 nm to 2 nm, suchas 1.5 nm to 2 nm, such as 1.8 nm.

The primary reflective coating 22 is formed over at least a portion ofthe second major surface 16, e.g., over at least a portion of thebasecoat 102, if present. The primary reflective coating 22 comprisesone or more inorganic or organic dielectrics, metals, or semiconductorsselected to reflect one or more portions of the electromagneticspectrum, such as one or more portions in the range of electromagneticsolar radiation. In one non-limiting embodiment, the primary reflectivecoating 22 comprises one or more radiation reflective metallic films orlayers. Examples of suitable reflective metals include, but are notlimited to, metallic platinum, iridium, osmium, palladium, aluminum,gold, copper, silver, or mixtures, alloys, or combinations thereof. Inone non-limiting embodiment, the primary reflective coating 22 comprisesa metallic silver layer having a thickness in the range of 50 nm to 500nm, such as 50 nm to 300 nm, such as 60 nm to 400 nm, such as 60 nm to300 nm, such as 70 nm to 300 nm, such as 80 nm to 200 nm, such as 80 nmto 150 nm, such as 90 nm to 150 nm, such as 90 nm to 140 nm, such as 90nm to 130 nm, such as 100 nm to 130 nm, such as 120 nm to 130 nm. In oneparticular non-limiting embodiment, the primary reflective coating 22comprises metallic silver and has a thickness of at least 50 nm, such asat least 60 nm, such as at least 70 nm, such as at least 80 nm (forexample, in the range of 70 nm to 90 nm). The primary reflective coating22 can be deposited to a thickness such that the article 1 has anyparticular desired level of reflectance in the desired range ofelectromagnetic radiation to be reflected. The primary reflectivecoating 22 can be deposited to a thickness sufficient that the primarycoating 22 is opaque in a desired wavelength range, such as visiblelight. The primary reflective coating 22 can be particularly useful inreflecting visible and solar infrared energy. In one particularnon-limiting embodiment, the primary reflective coating 22 is depositedby a conventional sputtering process, as described in more detail below.In another non-limiting embodiment, the primary reflective coating 22can comprise a “high reflector” comprising a plurality of alternatinghigh and low refractive index materials.

The protective coating 50 assists in protecting the underlying layers,such as the primary reflective layer 22, from mechanical and chemicalattack during manufacture, transit, handling, processing, and/or duringthe mirror's service life in the field. The protective coating 50 alsohelps protect the underlying layers from the ingress of liquid water,water vapor, and other environmental pollutants (be they solid, liquidor gas). The protective coating 50 can be an oxygen barrier coatinglayer to prevent or reduce the passage of ambient oxygen into theunderlying layers during subsequent processing, e.g., such as duringheating or bending. The protective coating 50 can be of any desiredmaterial or mixture of materials, such as but not limited to one or moreinorganic materials. In one exemplary embodiment, the protective coating50 can include a layer having one or more metal oxide materials, such asbut not limited to oxides of aluminum, silicon, or mixtures thereof. Forexample, the protective coating 50 can be a single coating layercomprising in the range of 0 wt. % to 100 wt. % alumina and/or 100 wt. %to 0 wt. % silica, such as 1 wt. % to 99 wt. % alumina and 99 wt. % to 1wt. % silica, such as 5 wt. % to 95 wt. % alumina and 95 wt. % to 5 wt.% silica, such as 10 wt. % to 90 wt. % alumina and 90 wt. % to 10 wt. %silica, such as 15 wt. % to 90 wt. % alumina and 85 wt. % to 10 wt. %silica, such as 50 wt. % to 75 wt. % alumina and 50 wt % to 25 wt. %silica, such as 50 wt. % to 70 wt. % alumina and 50 wt. % to 30 wt. %silica, such as 35 wt. % to 100 wt. % alumina and 65 wt. % to 0 wt. %silica, e.g., 70 wt. % to 90 wt. % alumina and 30 wt. % to 10 wt. %silica, e.g., 75 wt. % to 85 wt. % alumina and 25 wt. % to 15 wt. % ofsilica, e.g., 88 wt. % alumina and 12 wt. % silica, e.g., 65 wt. % to 75wt. % alumina and 35 wt. % to 25 wt. % silica, e.g., 70 wt. % aluminaand 30 wt. % silica, e.g., 60 wt. % to less than 75 wt. % alumina andgreater than 25 wt. % to 40 wt. % silica. In one particular non-limitingembodiment, the protective coating 50 comprises 40 wt. % to 15 wt. %alumina and 60 wt. % to 85 wt. % silica such as 85 wt. % silica and 15wt. % alumina. Other materials, such as aluminum, chromium, hafnium,yttrium, nickel, boron, phosphorous, titanium, zirconium, and/or oxidesthereof, can also be present, such as to adjust the refractive index ofthe protective coating 50. In one non-limiting embodiment, therefractive index of the protective coating 50 can be in the range of 1to 3, such as 1 to 2, such as 1.4 to 2, such as 1.4 to 1.8.

In one non-limiting embodiment, the protective coating 50 comprises acombination of silica and alumina. The protective coating 50 can besputtered from two cathodes (e.g., one silicon and one aluminum) or froma single cathode containing both silicon and aluminum. Thissilicon/aluminum oxide protective coating 50 can be written asSi_(x)Al_(1-x)O_(1.5+x/2), where x can vary from greater than 0 to lessthan 1. In one specific non-limiting embodiment, the protective coating50 can be a silicon/aluminum oxide coating (Si_(x)Al_(1-x)O_(1.5+x/2))having a thickness in the range of 5 nm to 5,000 nm, such as 5 nm to1,000 nm, such as 10 nm to 100 nm, e.g., 10 nm to 50 nm, such as 10 nmto 40 nm, such as 20 nm to 30 nm, such as 25 nm. Further, the protectivecoating 50 can be of non-uniform thickness. By “non-uniform thickness”is meant that the thickness of the protective coating 50 can vary over agiven unit area, e.g., the protective coating 50 can have high and lowspots or areas. In another non-limiting embodiment, the protectivecoating 50 comprises a silicon/aluminum oxide coating or mixture ofsilica and alumina, such as 85 wt. % silica and 15 wt. % alumina, andhas a thickness in the range of 10 nm to 500 nm, such as 20 nm to 300nm, such as 50 nm to 300 nm, e.g., 50 nm to 200 nm, such as 50 nm to 150nm, such as 50 nm to 120 nm, such as 75 nm to 120 nm such as 75 nm to100 nm. In a particular non-limiting embodiment, the protective coating50 can have a thickness of at least 50 nm, such as at least 75 nm, suchas at least 100 nm, such as at least 110 nm, such as at least 120 nm,such as at least 150 nm, such as at least 200 nm.

In another non-limiting embodiment, the protective coating 50 comprisessilica having a thickness in the range of 10 nm to 100 nm, such as 10 nmto 80 nm, such as 20 nm to 80 nm, such as 30 nm to 70 nm, such as 40 nmto 60 nm, such as 50 nm. In a further non-limiting embodiment, theprotective coating 50 comprises silica having a thickness in the rangeof 10 nm to 500 nm, such as 10 nm to 400 nm, such as 20 nm to 300 nm,such as 50 nm to 200 nm, such as 75 nm to 150 nm, such as 75 nm to 120nm.

In another non-limiting embodiment, the protective coating 50 cancomprise a multi-layer structure, e.g., a first layer with at least onesecond layer formed over the first layer. In one specific non-limitingembodiment, the first layer can comprise alumina or a mixture or alloycomprising alumina and silica. For example, the first layer can comprisea silica/alumina mixture having greater than 5 wt. % alumina, such asgreater than 10 wt. % alumina, such as greater than 15 wt. % alumina,such as greater than 30 wt. % alumina, such as greater than 40 wt. %alumina, such as 50 wt. % to 70 wt. % alumina, such as in the range of70 wt. % to 100 wt. % alumina and 30 wt. % to 0 wt. % silica, such asgreater than 90 wt. % alumina, such as greater than 95 wt. % alumina. Inone non-limiting embodiment, the first layer comprises all orsubstantially all alumina. In one non-limiting embodiment, the firstlayer can have a thickness in the range of greater than 0 nm to 1micron, such as 5 nm to 10 nm, such as 10 nm to 25 nm, such as 10 nm to15 nm. The second layer can comprise silica or a mixture or alloycomprising silica and alumina. For example, the second layer cancomprise a silica/alumina mixture having greater than 40 wt. % silica,such as greater than 50 wt. % silica, such as greater than 60 wt. %silica, such as greater than 70 wt. % silica, such as greater than 80wt. % silica, such as in the range of 80 wt. % to 90 wt. % silica and 10wt. % to 20 wt. % alumina, e.g., 85 wt. % silica and 15 wt. % alumina.In one non-limiting embodiment, the second layer can have a thickness inthe range of greater than 0 nm to 2 microns, such as 5 nm to 500 nm,such as 5 nm to 200 nm, such as 10 nm to 100 nm, such as 30 nm to 50 nm,such as 35 nm to 40 nm. In another non-limiting embodiment, the secondlayer can have a thickness in the range of greater than 0 nm to 1micron, such as 5 nm to 10 nm, such as 10 nm to 25 nm, such as 10 nm to15 nm. In another non-limiting embodiment, the protective coating 50 canbe a bilayer formed by one metal oxide-containing layer (e.g., a silicaand/or alumina-containing first layer) formed over another metaloxide-containing layer (e.g., a silica and/or alumina-containing secondlayer). The individual layers of the multi-layer protective coating canbe of any desired thickness. Non-limiting examples of suitableprotective coatings are described, for example, in U.S. patentapplication Ser. Nos. 10/007,382; 10/133,805; 10/397,001; 10/422,094;10/422,095; and 10/422,096.

As discussed above, the reflective article of the invention can includeone or more additional optional films, layers, coatings or structures.Additional reflective articles of the invention incorporating suchadditional structures will now be described. However, it is to beunderstood that the specific optional structures or coatings describedare not limited to the particular illustrated embodiments but that thesestructures could be utilized interchangeably in any of the embodimentsof the invention.

Another non-limiting reflective article incorporating features of theinvention is illustrated in FIG. 1B as a solar mirror 3. In theembodiment illustrated in FIG. 1B, the solar mirror 3 includes a ply 12with a first major surface 14, i.e. an outer major surface, and anopposed second major surface 16, i.e. an inner major surface, asdescribed above. An optional basecoat 102 can be provided over at leasta portion of one of the major surfaces, such as the second major surface16. A primary reflective coating 22 is formed over at least a portion ofthe second major surface 16, e.g. over at least a portion of thebasecoat 102, if present. One or more optional corrosion resistant oranti-corrosion coatings 104 can be provided, e.g., over at least aportion of the primary reflective coating 22. A primer film 106 can beprovided over or under at least a portion of the anti-corrosion coating104. A topcoat 40 can be provided over at least a portion of theanti-corrosion coating 104, e.g., over at least a portion of the primerfilm 106. A protective coating 50 can be provided over at least aportion of the topcoat 40. An optional encapsulation structure 24 can beprovided over at least a portion of the protective coating 50. Whileonly one anti-corrosion coating 104 is shown, the article could havemultiple anti-corrosion coatings 104 and multiple primer films 106either above and/or below the anti-corrosion coatings 104.

The ply 12, basecoat 102, primary reflective coating 22, and protectivecoating 50 can be as described above. However, in this embodiment, thereflective article 3 also comprises other layers having other functions.

For example, the anti-corrosion coating 104 can provide variousbenefits, such as corrosion inhibition and ultraviolet screeningbenefits. Also, the anti-corrosion coating 104 can provide some amountof electromagnetic energy reflection, which can permit a thinner primaryreflective layer 22 to be used. The anti-corrosion coating 104 can alsoprovide mechanical and/or chemical protection to the underlying coatinglayers. The anti-corrosion coating 104 can be provided under, over, orbetween one or more coating layers, e.g., the primary reflectivecoating(s) 22 or the top coat 40 (described below). Alternatively or inaddition thereto, the anti-corrosion coating 104 can be provided under,over, or between one or more layers of a protective coating 50. It isbelieved that the anti-corrosion coating 104 increases the corrosionresistance of the underlying coatings, and/or enhances the visible lightreflective of the solar mirror 3, and/or will block or reduce thepassage of UV radiation. Examples of suitable materials for theanti-corrosion coating 104 include, but are not limited to, elementalmetals and alloys of two or more metallic elements which are members ofGroups 2-16 of the Periodic Table of the Elements, including, but notlimited to, nickel and nickel-containing alloys, ferrous alloys andiron-containing alloys such as stainless steels, aluminum andaluminum-containing alloys, copper and copper-containing alloys,chromium and chromium-containing alloys, titanium andtitanium-containing alloys, brasses such as Naval brass (an alloy of Cu,Zn and Sn), Admiralty brass (an alloy of Zn, Sn and Cu), and Aluminumbrass (an alloy of Cu, Zn and Al), cobalt and cobalt-containing alloyssuch as alloys of cobalt and chromium, zinc and zinc-containing alloys,tin and tin-containing alloys, zirconium and zirconium-containingalloys, molybedenum and molybdenum-containing alloys, tungsten andtungsten-containing alloys, niobium and niobium-containing alloys,indium and indium-containing alloys, lead and lead-containing alloys,and bismuth and bismuth-containing alloys. Specific non-limitingembodiments include corrosion-resistant metals and metal alloysincluding, but not limited to, nickel and nickel-containing alloys suchas Nickel 200, Inconel(r) alloys such as Inconel 600 and Inconel 625,stainless steels such as stainless steel 304 and stainless steel 316,Monel(r) alloys such as Monel 400, Hastelloy(r) alloys, cobalt andcobalt-containing alloys such as Stellite(r) alloys, Inco alloys such asInco Alloy C-276 and Inco Alloy 020, Incoloy(r) alloys such as Incoloy800 and Incoloy 825, copper and copper-containing alloys such as brassesespecially Naval Brass (approximately 59% copper, 40% zinc, and 1% tin)and Admiralty Brass (approximately 69% copper, 30% zinc, 1% tin),silicon and silicon-containing alloys, titanium and titanium-containingalloys, and aluminum and aluminum-containing alloys such as aluminum6061. If present, the anti-corrosion coating(s) 104 can have any desiredthickness. In some non-limiting embodiments, the anti-corrosion coatings104 can have thicknesses in the range of, but not limited to, 1 nm to500 nm, such as 1 nm to 400 nm, such as 1 nm to 300 nm, such as 1 nm to200 nm, such as 1 nm to 100 nm, such as 10 nm to 100 nm, such as 20 nmto 100 nm, such as 30 nm to 100 nm, such as 40 nm to 100 nm, such as 50nm to 100 nm, such as 20 nm to 40 nm, such as 30 nm to 40 nm, such as 30nm to 35 nm. In other non-limiting embodiments, the anti-corrosioncoating(s) 104 can have a thickness of at least 10 nm, such as at least20 nm, such as at least 30 nm, such as at least 40 nm, such as at least50 nm, such as at least 100 nm, such as at least 200 nm. In oneparticular non-limiting embodiment, the anti-corrosion coating(s) 104comprise Inconel and can have a thickness in the range of 10 nm to 100nm, such as 10 nm to 80 nm, such as 15 nm to 50 nm, such as 20 nm to 40nm, such as 30 nm to 40 nm, such as 30 nm to 35 nm.

The optional primer layer 106 can be formed above and/or below theanti-corrosion coating(s) 104. The primer layer 106 is serves one orboth of the following functions: (a) a chemical getter for oxygen orother chemical species (either endogenous or exogenous to the article)such that they react with the primer layer(s) rather than the primaryreflective coating 22, and/or (b) a physical diffusion barrier toprevent chemical species from reaching and affecting (not necessarily bychemical reaction) the primary reflective coating 22. In one specificembodiment, the optional primer layer(s) 106 can comprise a metal ormetal alloy which has a strong affinity for oxygen and/or the chemicalreaction product of the metal or metal alloy with oxygen. The optionalprimer layer(s) 106 may also comprise materials which constitute adiffusion barrier so as to prevent the diffusion of molecular or atomicoxygen, water vapor, or other gaseous species from chemically reactingwith the primary reflective coating 22. In one particular embodiment,the primer layer 106 comprises titanium, titanium oxide, or amixture/combination thereof. In one particular embodiment, the primerlayer 106 can have a thickness in the range of 0.1 to 10 nm, such as 0.5to 5 nm, such as 0.5 to 4 nm, such as 0.5 to 2 nm, such as 1 nm to 2 nm.

The top coat 40 is formed over at least a portion of the primaryreflective coating 22, e.g., over at least a portion of theanti-corrosion layer 104, e.g., over at least a portion of the primerlayer 106. The top coat 40 can comprise one or more layers, e.g., one ormore dielectric layers, such as one or more metal oxides, nitrides,oxynitrides, borides, fluorides, or carbides. In one non-limitingembodiment, the topcoat 40 can be a single layer comprising a zinc andtin oxide, such as zinc stannate. In another particular non-limitingembodiment, the top coat 40 can comprise a multi-film structure, asdescribed below with respect to FIG. 1C. However, it is to be understoodthat the invention is not limited to oxide coatings. In one non-limitingembodiment, the topcoat 40 comprises zinc stannate. The top coat canhave a thickness of at least 10 nm, such as at least 20 nm, such as atleast 50 nm, such as at least 75 nm, such as at least 100 nm, such as atleast 150 nm, such as at least 200 nm. In one particular non-limitingembodiment, the top coat can have a thickness in the range of 5 nm to500 nm, such as 10 nm to 500 nm, such as 50 nm to 500 nm, e.g., 50 nm to300 nm, such as 100 nm to 250 nm, such as 100 nm to 200 nm, such as 120nm to 165 nm, such as 110 nm to 165 nm, such as 120 nm to 140 nm.Generally, the thicker the top coat, the more protection it provided tothe underlying coating layers.

The optional encapsulation structure 24 can be formed over and/or aroundat least a portion of the coated ply 12 described above. In onenon-limiting embodiment, the encapsulation structure 24 is formed atleast partly by an encapsulating material 92. Suitable encapsulatingmaterials 92 can include polymeric materials, inorganic materials, orcomposites, combinations, blends, mixtures, and alloys thereof. When asubstantial portion or all of the encapsulation material 92 comprises apolymeric material, the encapsulation material 92 may be deposited byany conventional means, such as but not limited to, brush coating, rollcoating, spray coating, curtain coating, dip coating, spin coating,knife-edge coating, screen printing, flood coating, electrocoating(a.k.a. electrodeposition), and powder coating. Suitable polymericencapsulating materials 92 include, but are not limited to,thermoplastics, thermosets, elastomers, and thermoplastic elastomersformed by addition polymerization or condensation polymerization, withor without cross-linking, and copolymers, composites, combinations,mixtures, blends, and alloys thereof. However, encapsulants comprisingpolymeric materials may employ various additives and fillers includinginitiators, photoinitiators, plasticizers, stabilizers, preservatives,biocides, flattening agents, flow agents, antioxidants, UV absorbers,surfactants, dyes, pigments, and inorganic or organic fillers. Potentialall-polymeric encapsulation materials may comprise, but are not limitedto, polyacrylates, polyalkyds, polyacrylnitriles, polyesters,polyfluorocarbons, polyvinyls, polyureas, polymelamines, andpolycarbonates. For example, the encapsulation structure 24 can includeacrylic-based coatings, urethane-based coatings, fluoropolymer and/orchlorofluoropolymer coatings (e.g. polyfluoroethylene,polychlorotrifluoroethylene, etc), polyvinylidene chloride-basedcoatings, ethylene vinyl alcohol-based coatings, polyacrylonitrile-basedcoatings, cyclic olefin polymers or copolymer-based coatings,inorganic/organic composite coatings: organic polymer matrix with one ormore inorganic phases (e.g. ceramics like silicon dioxide and aluminumoxide) dispersed within either uniformly or non-uniformly,plasma-sprayed inorganic coatings: ceramics (e.g. silicon dioxide,aluminum oxide, silicon nitride, titanium boride, titanium carbide,boron nitride, silicon carbide) and metals/metal alloys (aluminum,titanium, nickel-based alloys like Inconel, ferrous alloys likestainless steel), vulcanized butadiene-based coatings (e.g., syntheticrubber with sulfur crosslinking), UV-curable polysiloxane coatings,laminates comprising polymer interlayers (e.g. ethylene vinyl acetate orpolyvinylidene chloride interlayers) and glass back plates. In onenon-limiting embodiment, the polymeric material is free of heavy metals,such as lead. For encapsulants comprising all inorganic materials,suitable materials include, but are not limited to, metals, metalalloys, or ceramics and composites or combinations thereof. Examples ofsuitable processes to deposit such inorganic encapsulants includephysical vapor deposition (e.g. sputter deposition, electron beamevaporation, thermal evaporation, cathodic arc deposition, plasma spraydeposition, flame spray deposition, pyrolytic spray deposition,ion-assisted deposition), chemical vapor deposition (e.g. thermal CVD,plasma-assisted/plasma-enhanced CVD), sol-gel deposition, otherwet-chemical processes (e.g. ceramic enamels), and combinations thereof.Further, the encapsulating structure 24 may comprise both polymeric andinorganic materials in combination.

Specific coatings suitable for the encapsulation structure 24 include,but are not limited to, the Corabond® family of coatings (such asCorabond® HC7707 coating) commercially available from PPG Industries,Inc. of Pittsburgh, Pa., Ferro GAL-1875 “Etch” ceramic enamel,Cosmichrome® coating (commercially available from Gold Touch, Inc.),Sureguard® mirror backing coating (commercially available from SpraylatCorporation), EcoBrite® ink coatings (commercially available from PPGIndustries, Inc), PRC 4429 and PRC 4400 coatings commercially availablefrom PRC DeSoto, and Spraylat Lacryl Series 700 or 800 coatings(available from Spraylat Corporation). Alternatively, the encapsulatingstructure 24 could be metallic, such as formed by one or more metalliclayers, such as those described above with respect to the anti-corrosioncoating 104, formed over the second reflective coating 22 with anoptional polymeric material formed over the metallic layer(s).Additional examples of non-polymeric/inorganic encapsulants includeceramic enamels, sol-gel ceramic coatings, flame-sprayed ceramic ormetallic coatings, plasma-sprayed ceramic or metallic coatings, andcathodic arc-sprayed ceramic or metallic coatings. In one specificnon-limiting embodiment, the encapsulation structure 24 can be amulti-layer structure, such as a bilayer coating having a lowlead-containing or lead free basecoat and a low lead-containing or leadfree topcoat.

A further non-limiting solar mirror 10 incorporating features of theinvention is illustrated in FIG. 1C. In the embodiment illustrated inFIG. 1C, the solar mirror 10 includes a first ply 12 with a first majorsurface 14, i.e. an outer major surface, and an opposed second majorsurface 16, i.e. an inner major surface, as described above. In onenon-limiting embodiment, an optional secondary reflective coating 20 isformed over at least a portion of the inner surface 16. In anothernon-limiting embodiment, the optional secondary reflective coating 20can be formed over at least a portion of the outer major surface 14. Aprimary reflective coating 22 is formed over at least a portion of thesecond major surface 16, e.g. over at least a portion of the secondaryreflective coating 20 if the secondary reflective coating 20 is presentand on the second major surface 16. An anti-corrosion coating 104 can beformed over at least a portion of the primary reflective coating 22. Atop coat 40 can be formed over at least a portion of the anti-corrosioncoating 104. A protective coating 50 can be formed over at least aportion of the top coat 40. The mirror 10 can also include anencapsulating structure 24.

The optional secondary reflective coating 20, if present, can provideone or more functions in the solar mirror 10. In one non-limitingembodiment, the secondary reflective coating 20 can be selected toenhance the overall electromagnetic radiation reflection of thereflective article in a particular area or range of electromagneticradiation. The secondary reflective coating 20 can be selected ordesigned to enhance the reflection of electromagnetic radiation in oneor more portions of the electromagnetic spectrum (e.g. visible,infrared, ultraviolet). In one non-limiting embodiment, the secondaryreflective coating 20 can be selected to enhance the reflection of shortwavelength radiation, such as less than 600 nm, such as less than 550nm, such as in the range of 400 nm to 550 nm. Alternatively, thesecondary reflective coating 20 can be tuned, such as by varying itsthickness, to reflect UV radiation. The secondary reflective coating 20can comprise one or more layers of reflective material, such as one ormore layers of metal oxide materials. In one specific non-limitingembodiment, the secondary reflective coating 20 comprises alternatinglayers of a relatively high refractive index material and a relativelylow refractive index material. A “high” refractive index material is anymaterial having an index of refraction higher than that of the “low”refractive index material. In one non-limiting embodiment, a lowrefractive index material is a material having an index of refraction ofless than or equal to 1.75. Non-limiting examples of low refractiveindex materials include silica, alumina, fluorides (such as magnesiumfluoride and calcium fluoride) and alloys, mixtures or combinationsthereof. In one non-limiting embodiment, a high refractive indexmaterial has an index of refraction greater than 1.75. Non-limitingexamples of such materials include titania, zirconia, zinc stannate,silicon nitride, zinc oxide, tin doped zinc oxide, niobium oxide,tantalum oxide, and alloys, mixtures and combinations thereof. Thesecondary reflective coating 20 can be, for example but not limiting tothe present invention, a multi-layer coating as shown in FIG. 1C havinga first layer 26, e.g., a first dielectric layer, and a second layer 28,e.g., a second dielectric layer. In one non-limiting embodiment, thefirst layer 26 has a high refractive index and the second layer 28 has alow refractive index. In one non-limiting embodiment, the first layer 26comprises titania and the second layer 28 comprises silica. In onespecific non-limiting embodiment, the first layer, e.g., titania, has athickness in the range of 15 nm to 35 nm, such 20 nm to 30 nm, such as22 nm to 27 nm, such as 25 nm. The second layer, e.g., silica, can havea thickness in the range of 30 nm to 60 nm, such 35 nm to 50 nm, such as40 nm to 50 nm, such as 42 nm. It is to be understood that the materialsof the secondary reflective coating 20 are not limited to metal oxides.Any materials, such as but not limited to oxides, nitrides, oxynitrides,fluorides, etc. could be utilized.

In the non-limiting embodiment shown in FIG. 1C, an optional adhesivelayer 30 can be provided between the secondary reflective coating 20 andthe primary reflective coating 22. The adhesive layer 30 can be anylayer that enhances the adhesion between the secondary and primaryreflective coatings 20, 22 or improves the mechanical and/or chemicaldurability of the secondary or primary reflective coatings 20, 22. Theadhesive layer 30 can comprise at least one material selected fromdielectrics, semiconductors, polymers, organics, or layers of metal ormetal alloys. In one non-limiting embodiment, the adhesive layer 30comprises at least one material selected from oxides, nitrides, oroxynitrides of zinc, tin, titanium, or combinations thereof, such as butnot limited to zinc oxide, titania, or a zinc/tin oxide such as zincstannate. For example, the adhesive layer 30 can have a thickness ofless than or equal to 5 nm, such as less than or equal to 4 nm, such asless than or equal to 3 nm, such as less than or equal to 2 nm, such asless than or equal to 1 nm.

In the illustrated exemplary embodiment shown in FIG. 1C, the top coat40 is formed over at least a portion of the primary reflective coating22. The top coat 40 can be as described above. In one specificnon-limiting embodiment, the topcoat can comprise one or more layers,e.g., one or more dielectric layers, such as one or more metal oxides,nitrides, oxynitrides, borides, fluorides, or carbides. In oneparticular non-limiting embodiment, the top coat 40 comprises amulti-film structure having a first film 42, e.g., a metal oxide film, asecond film 44, e.g., a metal alloy oxide or oxide mixture film, andoptionally a third film 46, e.g., a metal oxide film. However, it is tobe understood that the invention is not limited to oxide coatings andthat other coatings, such as but not limited to nitrides or oxynitrides,could be used. In one non-limiting embodiment, the topcoat 40 cancomprise zinc oxide or a zinc/tin oxide, such as zinc stannate, and canhave a thickness in the range of 1 nm to 500 nm, such as 5 nm to 500 nm,such as 10 nm to 500 nm, such as 50 nm to 500 nm, e.g., 50 nm to 300 nm,such as 100 nm to 250 nm, such as 100 nm to 200 nm, such as 120 nm to165 nm.

In one non-limiting embodiment, the first film 42 can be azinc-containing film, such as zinc oxide. The zinc oxide film can bedeposited from a zinc cathode that includes other materials to improvethe conductivity and sputtering characteristics of the cathode. Forexample, the zinc cathode can include a small amount (e.g., 10 wt. % orless, such as 0 wt. % to 5 wt. %) of a conductive material, such as tin,to improve the sputtering characteristics of the cathode. In which case,the resultant zinc oxide film would include a small percentage of tinoxide, e.g., 0 to 10 wt. % tin oxide, e.g., 0 to 5 wt. % tin oxide. Acoating layer deposited from a zinc cathode having 10 wt. % or less tinis referred to herein as “a zinc oxide” layer even though a small amountof the tin (e.g. 10 wt. %) may be present. The small amount of tin inthe cathode is believed to form a small amount of tin oxide in thepredominantly zinc oxide-containing film. In one non-limitingembodiment, the zinc oxide first film 42 comprises 90 wt. % zinc and 10wt. % tin and has a thickness in the range of 1 nm to 200 nm, such as 1nm to 150 nm, such as 1 nm to 100 nm, such as 1 nm to 50 nm, such as 1nm to 25 nm, such as 1 nm to 20 nm, such as 1 nm to 10 nm, such as 2 nmto 8 nm, such as 3 nm to 8 nm, such as 4 nm to 7 nm, such as 5 nm to 7nm, such as 6 nm.

In one non-limiting embodiment, the second film 44 can be a zinc/tinalloy oxide or zinc/tin oxide mixture film. The zinc/tin alloy oxide canbe that obtained from magnetron sputtering vacuum deposition from acathode of zinc and tin that can comprise zinc and tin in proportions of10 wt. % to 90 wt. % zinc and 90 wt. % to 10 wt. % tin. One suitablemetal alloy oxide that can be present in the second film 44 is zincstannate. By “zinc stannate” is meant a composition ofZn_(X)Sn_(1-X)O_(2-X) (Formula 1) where “x” varies in the range ofgreater than 0 to less than 1. For instance, “x” can be greater than 0and can be any fraction or decimal between greater than 0 to lessthan 1. For example where x=2/3, Formula 1 is Zn_(2/3)Sn_(1/3)O_(4/3)which is more commonly described as “Zn₂SnO₄”. A zincstannate-containing film has one or more of the forms of Formula 1 in apredominant amount in the film. In one non-limiting embodiment, a zincstannate second film 44 can have a thickness in the range of 1 nm to 200nm, such as 1 nm to 150 nm, such as 1 nm to 100 nm, such as 1 nm to 50nm, such as 1 nm to 25 nm, such as 1 nm to 20 nm, such as 5 nm to 15 nm,such as 6 nm to 14 nm, such as 8 nm to 14 nm, such as 10 nm to 14 nm,such as 11 nm to 13 nm, such as 12 nm.

In one non-limiting embodiment, the optional third film 46 can be zinccontaining film similar to the first film 42, e.g., a zinc oxide film.In one non-limiting embodiment, the optional zinc oxide third film 46has a thickness in the range of 1 nm to 200 nm, such as 1 nm to 150 nm,such as 1 nm 100 nm, such as 1 nm to 50 nm, such as 1 nm to 25 nm, suchas 1 nm to 10 nm, such as in the range of 2 nm to 8 nm, such as in therange of 3 nm to 8 nm, such as in the range of 4 nm to 7 nm, such as inthe range of 5 nm to 7 nm, such as 6 nm.

In one non-limiting embodiment, the solar mirror 10 can have aphotoactive coating 60, such as a photocatalytic and/or photohydrophiliccoating, formed over at least a portion of the first surface 14. Anon-limiting example of one suitable material for the photoactivecoating 60 is titania. The photoactive coating 60 can be depositeddirectly on the first surface 14 or a barrier layer, such as a sodiumion diffusion barrier (SIDB) layer 64 can be provided between the firstsurface 14 and the photoactive coating 60. A non-limiting example of asuitable SIDB layer material is silica or alumina or combinationsthereof. Alternatively, the photoactive coating 60 can be eliminated andjust the SIDB layer formed over the first surface 14.

Some or all of the coatings described above for the reflective articlesof the invention can be deposited by any conventional method, such asbut not limited to wet chemical methods (e.g. precipitation of thecoating from solution, electroless plating, sol-gel chemistry, etc.),electrochemical methods (e.g. electroplating/electrodeposition), sputterdeposition (e.g. magnetron sputter vapor deposition (MSVD)), evaporation(e.g. thermal or electron beam evaporation), chemical vapor deposition(CVD), spray pyrolysis, flame-spraying, or plasma-spraying In onenon-limiting embodiment, some or all of the coatings can be deposited byMSVD. Examples of MSVD coating devices and methods will be wellunderstood by one of ordinary skill in the art and are described, forexample, in U.S. Pat. Nos. 4,379,040; 4,861,669; 4,898,789; 4,898,790;4,900,633; 4,920,006; 4,938,857; 5,328,768; and 5,492,750. For example,the primary reflective coating 22 can be applied by wet chemical methods(e.g. “wet-silver” deposition—precipitation of silver from silvernitrate solution), if desired. In one non-limiting embodiment, one ormore layers of the secondary reflective coating 20 can be applied byconventional CVD methods, for example on a float glass ribbon while theribbon is in the tin bath. The primary reflective coating 22 and one ormore layers of the top coat 40 can then be applied by a differentprocess, such as MSVD. Alternatively, all of the coatings can be appliedby the same process, such as by MSVD. It is believed that applying atleast some of the coatings by sputtering has advantages over many othertechniques. For example, it is possible to deposit a wide range ofmaterials in a single vacuum chamber. Also, sputter deposition isexpected to yield layers having higher chemical purity than conventionalwet chemistry methods. Further, sputtering eliminates the liquid wastestream produced from wet chemical methods and also enables other metalsto be easily deposited. Moreover, sputtering allows inorganic oxides tobe deposited to be used for adhesion layers, chemical barriers andmechanical protection.

The encapsulation structure 24 can be formed over and/or around at leasta portion of the coated ply described above. The encapsulation structure24 is not limited to the examples described above but could include anymaterial to protect the underlying coating materials from chemical andor mechanical attack. For example, in the solar mirror 80 shown in FIG.2, the encapsulation structure 24 includes a second ply 82 connected tothe first ply 12, e.g., to the protective coating 50, by a polymericlayer 84. The second ply 82 can be selected from the materials describedabove for the first ply 12 and can be the same or different from thefirst ply 12. Additionally, the second ply 82 need not be transparent toelectromagnetic radiation in any portion of the electromagneticspectrum.

The polymeric layer 84 can be of any desired material and can includeone or more layers or plies. The layer(s) 84 may comprisethermoplastics, thermosets, elastomers, and/or thermoplastic elastomers.The layer 84 can be a polymeric or plastic material, such as, forexample, polyvinylbutyral, plasticized polyvinyl chloride, ormulti-layered thermoplastic materials includingpolyethyleneterephthalate, ethylene vinyl acetate (EVA), polyvinylchloride, polyvinylidene chloride, polycarbonate, polyacrylates (e.g.polymethylmethacrylate, polyacrylonitrile), polysiloxanes,fluoropolymers, polyesters, melamines, polyureas, polyurethanes,polyalkyds, polyphenol formaldehydes, etc. Suitable materials aredisclosed in, but are not limited to, U.S. Pat. Nos. 4,287,107 and3,762,988. The layer 84 secures the first and second plies together, canprovide energy absorption, and can increase the strength of thelaminated structure. In one non-limiting embodiment, the layer 84 ispolyvinylbutyral and has a thickness in the range of 0.5 mm to 1.5 mm,such as 0.75 mm to 0.8 mm.

In the solar mirror 90 of the invention shown in FIG. 3, a polymericencapsulation structure 24 formed at least partly by an encapsulatingmaterial 92 as described above can be used. The encapsulating material92 can wrap around at least part of the sides (minor surfaces) of thesolar mirror 90 providing an edge seal for the article. Alternatively, aconventional edge sealant, such as but not limited to polyvinylidenechloride (PVDC), can be applied to the edges, i.e., minor surfaces, ofthe article before the encapsulating material is applied.

Another solar mirror 100 of the invention is shown in FIG. 4. The solarmirror 100 includes a first ply 12 as described above. In thisembodiment, the secondary reflective coating 20 is absent. The primaryreflective coating 22 can be applied over at least a portion of thesecond major surface 16. In one particular embodiment, a basecoat 102 isprovided between the second major surface 16 and the primary reflectivecoating 22. The basecoat 102 can be the same as described above.

In this embodiment, the primary reflective coating 22 can be any of thematerials described above with reference to the earlier embodiments. Inone particular embodiment, the primary reflective coating 22 comprisesmetallic silver having a thickness in the range of 10 nm to 500 nm, suchas 50 nm to 500 nm, such 50 nm to 300 nm, such as 50 nm to 200 nm, suchas 100 nm to 200 nm, such as 100 nm to 150 nm, such as 110 nm to 140 nm,such as 120 nm to 140 nm, such as 128 nm to 132 nm. In anotherparticular embodiment, the primary reflective coating 22 comprisesmetallic silver having a thickness in the range of 1 nm to 500 nm, suchas 50 nm to 500 nm, such 50 nm to 300 nm, such as 50 nm to 200 nm, suchas 50 nm to 150 nm, such as 70 nm to 150 nm, such as 90 nm to 120 nm,such as 90 nm to 130 nm, such as 90 nm to 100 nm, such as 90 nm to 95nm.

The top coat 40 can be a single layer or a multi-layer structure havinga first layer 110 and a second layer 112. In one particular embodiment,the first metal oxide layer 110 comprises zinc oxide having a thicknessin the range of 1 nm to 30 nm, such as 1 nm to 25 nm, such as 5 nm to 20nm, such as 10 nm to 20 nm, such as 10 nm to 17 nm. The second layer 112comprises zinc stannate having a thickness in the range of 10 nm to 100nm, such as 40 nm to 45 nm.

The solar mirror 100 can also include a protective coating 114 which canbe the same or similar to the protective coating 50 described above. Inone particular embodiment, the protective coating 114 comprises silicahaving a thickness in the range of 10 nm to 500 nm, such as 10 nm to 300nm, such as 10 nm to 100 nm, such as 20 nm to 100 nm, such as 30 nm to80 nm, such as 40 nm to 60 nm, such as 50 nm to 60 nm, such as 57 nm.

FIG. 5 shows a reflective article of the invention (e.g., a solar mirror1, 3, 10, 80, 90, 100) of the invention mounted on a support base 120.The reflective article is mounted such that the first major surface 14faces outwardly. The reflective article can be mounted in anyconventional method, such as by an adhesive or by securing the articlemechanically in a frame, just to name a few. The base 120 can beconnected to the encapsulating structure 24 as described above.Alternatively, the encapsulating structure 24 can be eliminated and thebase 120 connected with the outer coating layer of the coating stack,e.g., the protective coating 50. The base 120 can be of any desiredmaterial, such as, but not limited to metal (such as aluminum, stainlesssteel, etc.) or a polymeric material, such as plastic.

The invention provides highly reflective articles that are useful inmany applications, such as but not limited to solar mirrors. Thereflective articles of the invention can have a hemisphericalsolar-weighted, integrated Rg reflectance (WIRg) of at least 50%, suchas at least 60%, such as at least 70%, such as at least 80%, such as atleast 90%, such as at least 91%, such as at least 92%, such as at least93%, such as at least 94%, such as at least 95%, such as in the range of90% to 96%.

Corrosion Protection

As discussed above, the reflective articles, particularly in the form ofoutdoor solar mirrors, can be exposed to harsh environmental conditions.The metallic reflective layer(s) of the solar mirror can corrode orbecome tarnished when exposed to atmospheric moisture, hydrogen sulfide,atmospheric chloride, and the like. Corrosion or tarnishing of thereflective metallic layer decreases the solar reflectance of the mirrorand reduces the commercial lifetime of the mirror.

In order to address this problem, reflective articles of the inventioncan include a cathodic protection system to reduce corrosion of themetallic layer.

FIG. 6 illustrates a passive cathodic protection system 200 attached toa reflective article 202 in the form of a solar mirror. The reflectivearticle 202 can be of any of the types described above and can includeany of the layer structures described above. For purposes ofillustration, the reflective article 202 includes a ply 12 having aprimary reflective coating 22 comprising one or more metallic layers,and a protective coating 50. An encapsulation structure 24 is formed onthe coated ply 12 and the coated ply 12 and encapsulation structure 24are optionally attached to a support base 120. Only one primaryreflective coating 22 is illustrated in FIG. 6 for ease of discussion.However, it is to be understood that the reflective article 202 couldincorporate any number of reflective coatings 22 or any of the othercoatings described above with respect to the other embodiments of thereflective articles.

A contact or conductor 204 is in electrical contact with the metalliclayer(s) of the reflective coating 22. For example, the conductor 204can extend along a periphery of the coating stack and is in electricalcontact with the metallic layer(s) of the metallic reflective coating22. The conductor 204 can be, for example, a metal foil or mesh made ofa conductive material, such as copper, zinc, magnesium, or the like. Theconductor 204 is electrically connected to a sacrificial anode 206 inany conventional manner, such as by a conventional wire 208 or anysimilar electrically conductive element. In the illustrated embodiment,the anode 206 is shown attached to the support body 120. However, thisis simply one configuration of the invention and the anode 206 could beplaced anywhere on or near the reflective article 202.

The contact/conductor 204 and connector/wire 208 used to make theelectrical connection to the sacrificial anode 206 can comprise anyelectrically-conductive material including the case where the samematerial is used for all three elements (204, 206, and 208). But, inthat case, the conductor 204 and connector 208 will also corrode and besacrificial. Therefore, elements 204 and 208 would also have to bereplaced eventually. For example, one could make the contact/conductor204 and the sacrificial anode 206 the same element by attaching stripsor foils of a sacrificial material to one or more edges (“sidewalls”),or to the rear face, of the mirror. Alternatively, the conductor 204 andconnector 208 can be chosen to comprise a material (e.g. gold, platinum,etc.) that is more noble than the material(s) comprising the metallicreflective layer(s) of the reflective coating 22 and more noble than thematerial comprising the sacrificial anode 206 so that the sacrificialanode 206 will function as intended. Further, there is: (a) an electronconduction path between the sacrificial anode 206 and the materials ofthe metallic layer(s), and (b) an ion conduction path between the two.The electron conduction path is achieved by ensuring there is electricalcontinuity between the sacrificial anode 206 and the materialscomprising the metallic reflective layer(s), such as via the conductor204 and connector/conductor 208. The ion conduction path can comprise anelectrolytic medium which electrically connects the sacrificial anode206, connector 208, conductor 204, and metallic reflective layer(s),such as is provided by one or more layers of water vapor molecules whichare expected to be typically adsorbed on the surfaces of theaforementioned elements. Of course, a layer of liquid water, such as dueto rainwater or condensation of dew, also functions as a suitableelectrolytic medium. Alternatively, one could intentionally apply anelectrolytic material (e.g. an electrolytic gel or a polymerelectrolyte) to the surfaces of the aforementioned elements to ensurethat an ion conduction pathway is maintained between the sacrificialanode 206 and the material(s) of the metallic reflective layer(s).

Electrical contact to the (electrically-conductive) reflective layer(s)of the reflective coating 22 can be made via any electrically-conductivematerial (e.g., electrically conductive thin film coating, conductivepaint e.g., “silver paint”, or conductive adhesive, conductive tape orfoil, conductive ceramic enamel, etc.) applied/deposited on the“sidewall” of the substrate, such that there is electrical continuitybetween the metallic layer(s) of the reflective coating 22 of the mirrorcoating and: (a) the sacrificial anode (for “passive” cathodicprotection), or alternatively (b) the (DC) negative terminal of a powersupply, battery, photovoltaic module, DC-rectified-output of an ACgenerator (e.g. turbine generator connected to a windmill, etc.) for“active” cathodic, protection described below. There is electricalcontinuity between the metallic layer(s) and a source of electrons whichis at a negative electrical potential relative to the metallic layer(s).These electrons are supplied via the corrosion of a sacrificial anode(passive system) or via a power supply (active system). Any method ofmaking electrical contact between such a source of electrons and themetallic layer(s) is suitable. For example, one can make electricalcontact to the “face” of the mirror coating, in contrast to theedge/sidewall of the coating, either below the encapsulation structure(or via the encapsulation structure, if the encapsulant is electricallyconductive) by clamping a conductive electrical clip/lead to themirror's coated face. Or, one could apply an electrically conductivepaint or conductive adhesive or conductive solder or conductive ceramicenamel to the mirror's coated face and then attach an electrical lead tothat material so as to make electrical contact between the mirrorcoating's metallic layer(s) and the sacrificial anode or powersupply/source of electrons. Indeed, one could even clamp or solder orglue (using an electrically-conductive adhesive/paint) a metal foil(e.g. Zn, Mg, Al₁ Cu) to the coated surface of the mirror using anelectrically-conductive clip or electrically-conductive adhesive/paintsuch that the foil covers all or a portion of the mirror coating.Indeed, the sacrificial anode could even comprise a layer of metallicZn, Mg, Al, or Cu integrated into the mirror coating itself.

As will be appreciated by one skilled in the art, the anode 206 is amaterial comprising a metal that is higher in the electromotive seriesthan the metal layer(s) of the primary reflective coating 22. Due to thedifference in electrical potential between the cathodically protectedmetal of the reflective coating 22 and the sacrificial anode 206, theanode 206 has a surplus of electrons and, therefore, corrosion willoccur at the anode not the cathode. Such a cathodic protection systemwill protect the corrodible metal layer(s) of the reflective coating 22as long as a sufficient amount of sacrificial anode metal remains tosupply electrons to the protected structure. When the anode 206 isnearly completely corroded, it can be replaced by another anode 206 toallow the cathodic protection system to continue its function.

The particular material of the anode 206 can be selected based on themetal used in the metallic layer(s) of the reflective coating 22. Forexample, if the reflective coating 22 incorporates one or more metallicsilver layers, the anode 206 can be formed of material, such as copper,zinc, manganese, etc. having a greater oxidation potential than silver.As would be appreciated by one skilled in the art, should the metallicsilver layer of the reflective coating 22 be exposed to potentialcorrosion inducing materials, the anode 206 will preferentially corroderather than the silver layer and, thus, enhance the commercial lifetimeof the solar mirror. The sacrificial anode 206 should not be inelectrical contact with another electrically conductive body. Thesacrificial anode 206 should be in electrical contact with the metalliclayer(s) of the mirror coating one wishes to protect from corrosion. Forexample, if the support base 120 is electrically conductive (e.g., apiece of corrugated steel) the sacrificial anode 206 should beelectrically insulated from the support base 120 (such as by anon-conductive shield or material) or the anode 206 could be separatedfrom the support base 120.

An active (impressed current) cathodic protection system can also beincorporated into or attached to a reflective article of the invention.FIGS. 7-9 illustrate an exemplary active cathodic protection system 216attached to a reflective article 202 as described above. The activecathodic system 216 includes one or more solar panels 218 (or othersource of electrons) electrically connected to the metallic reflectivelayer 22 of the solar mirror 202 and to a suitable anode 206′, such asby wires 219 and 221, respectively. The solar panel 218 can be aconventional solar panel formed by an interconnected assembly ofphotovoltaic cells or solar cells in the form of a photovoltaic array.The solar panel generates electricity using light energy through thephotovoltaic effect. The negative terminal(s) of the solar panel 218 isconnected to the metal layer(s) of the reflective coating 22, such asthrough one or more contacts or conductors 204′. The positiveterminal(s) of the solar panel 218 is connected to the anode 206′. Inthis system, a negative electrical bias is provided to the metalliclayer(s) of the reflective coating 22. If oxidizing or corroding agentsattack the metal layer(s), the extra electrons provided by the solarpanel 218 are consumed rather than oxidation of the metallic layer(s). Aregulator can be provided to establish and maintain a desired directcurrent (DC) voltage level at the output terminals of the solar panel218. The protection system 216 can also include an electrical storagedevice, such as a battery 220. The battery 220 is connected to the solarpanel 218 via a wire 222. The battery 220 is connected to the anode 206′by a wire 224 and the negative terminal is connected to the metalliclayer by a wire 226 and an optional connector 204″. A conventionalopen/closed switch 228 can be connected to the wire 224 and another suchswitch 230 can be connected to the wire 226. A regulator can be providedto establish and maintain a desired DC voltage level at the outputterminals of the battery 220. As will be appreciated by one skilled inthe art, the “active” cathodic protection system need not employ solarpanels. Any means of supplying electrons (e.g. battery, power supply,etc.) to the material(s) to be protected can be employed. For example, aconventional battery could just be connected to the metal layer(s) ofthe reflective coating 22 to supply electrons to prevent corrosion ofthe metal layer(s). Also, the anode 206′ need not be the same as for thepassive system described above. In the “active” approach, electrons aresupplied to the material(s) to be protected by a power supply, such as abattery, etc., rather than by corrosion/oxidation of a sacrificialanode. Indeed, the positive terminal of the electron source (solarpanel, battery, etc.) can be electrically grounded to the earth suchthat the anode is simply the earth.

In the illustrated embodiment, under normal operation during daylighthours, a portion of the electricity generated by the solar panel(s) 218is provided to maintain the impressed voltage to the metallic layer(s).The remainder of the electricity generated by the solar panel 218 isdirected to the battery 220 via the wire 222 for storage. The switches228 and 230 are open so that the solar panel 218 provides the impressedcurrent cathodic protection to the metallic layer(s), while at the sametime a portion of the electricity generated by the solar panel 218 isbeing stored in the battery 220. During bad weather or at night, theswitches 228 and 230 are closed so that the battery 220 provides theimpressed voltage to the metallic layer(s). The switches 228 and 230 canbe operated in any conventional manner, such as by timers or by beingconnected to a central processing unit or similar remote control device.

It is preferred that the voltage supplied to the metallic layer(s) ofthe reflective coating 22 be sufficient to prevent corrosion of themetal of the metallic layer(s). For example, the supplied voltage can beregulated to be greater than 5 volts (V), such as at least 6 V, such asat least 7V, such as at least 8V, such as at least 9V, such as at least10V, such as at least 12V, such as at least 15V. For example, thesupplied voltage can be in the range of 8V to 15V, such as 10V to 15V.

FIGS. 8 and 9 show one exemplary embodiment of a reflective article 202with solar panels 218 extending outwardly from a perimeter of thereflective article 202. The solar panels 218 can be connected to theencapsulation structure 24, to the support base 120, or can be locatedon the ground adjacent to the solar mirror 202. While the solar panels218 are shown only on three sides of the article 202, it is to beunderstood that this is just one exemplary embodiment and the solarpanels 218 could be on one or more sides of the mirror 202, such as onone to four sides of the mirror 202.

As described above and as shown in the following Examples, an advantageof the reflective article of the invention over conventionalwet-chemical mirrors is that the reflective article of the invention canbe coated and then heated to a temperature sufficient to heat, treat, orbend the coated article (prior to the application of any polymericencapsulating structure) without adversely impacting upon thereflectance of the article. Also, coatings of the invention can exhibitan improvement in spectral performance (i.e., an increase in reflectanceover some or all of the measured spectral range) and an increase insolar-weighted integrated reflectance after heating. For example, areflective article of the invention having basecoat and/or primaryreflective coating and/or secondary reflective coating and/oranti-corrosion coating and/or topcoat and/or protective coating can beheated to a temperature sufficient to bend or heat treat the articleprior to application of the encapsulation structure. For example, thesubstrate and coatings could be heated to at least 300° F. (149° C.),such as at least 350° F. (177° C.), such as at least 400° F.(204° C.),such as at least 500° F. (260° C.), such as at least 750° F. (399° C.),such as at least 800° F. (427° C.), such as at least 900° F. (482° C.),such as at least 1000° F. (538° C.), such as at least 1022° F. (550°C.), such as at least 1100° F. (593° C.), such as at least 1200° F.(649° C.), such as at least 1300° F. (704° C.), such as in the range of350° F. (177° C.) to 1300° F. (704° C.).

The invention will now be described with respect to specific examplesillustrating various mirror structures incorporating various aspects ofthe invention. However, it is to be understood that the invention is notlimited to these specific examples.

EXAMPLES

Table 1 shows the structure for various mirrors (Samples 1-10) of theinvention.

TABLE 1 Sample T_(i) Inconel T_(i) S_(i)85/ No. Ag Primer T_(i)O₂ ZnOZr₂SnO₄ 600 Primer T_(i)O₂ ZnO Zn₂SnO₄ Al15 1 1.5 130 2.5 0 12 10 33 0 00 0 60 2 1.5 130 2.5 0 9 10 0 0 0 9 0 60 3 1.5 120 1.5 0 12 10 33 0 0 00 60 4 1.5 120 1.5 0 9 10 0 0 0 0 0 60 5 1.5 120 1.5 0 0 0 0 0 0 10 2160 6 1.5 120 0 0 0 0 33 0 0 10 12 60 7 1.5 120 0 0 0 0 33 0 0 0 0 60 81.5 120 1.5 0 5 21 33 0 0 0 0 60 9 1.8 127 1.6 1.8 0 0 33 0 0 17 42 5710 1.8 132 0 0 0 0 20 1 0 10 42 57 11 1.6 128 0 0 0 0 33 1 0 0 48 111 122 128 0 0 0 0 33 1 0 0 110-120 85-120 13 2 128 0 0 0 0 33 1 0 0 120-16575-120 14 2 91 0 0 0 0 31 1 0 0 153 100 15 2 95 0 0 0 0 33 1 0 0 137 76

Table 2 shows the hemispherical WIRg reflectance (hemisphericalsolar-weighted, integrated Rg reflectance) of the mirrors of Samples1-15 before and after heating. From these results, it appears that thehemispherical solar-weighted integrated reflectance of mirrors of theinvention can increase upon heating. The “Softening Point” column meansthat the coated articles were placed in an oven at 1300° F. (704° C.)and heated (about 5 minutes) to the softening point of the glass (themaximum temperature of the coated surface was approximately 1185° F.(641° C.).

TABLE 2 As Deposited 30 mins Softening (unheated) @ 350° F. (177° C.)Point Sample ASTM G-173- ISO ASTM G-173- ISO ASTM G-173- ISO No.3AM-1.5D 9050 3AM-1.5D 9050 3AM-1.5D 9050 1 92.9 92.7 93.6 93.4 93.192.8 2 92.6 92.4 93.5 93.3 94.2 94.1 3 Not Not Not Not Not Not MeasuredMeasured Measured Measured Measured Measured 4 Not Not Not Not Not NotMeasured Measured Measured Measured Measured Measured 5 92.8 92.6 93.493.3 93.8 93.6 6 92.8 92.6 93.4 93.3 93.9 93.8 7 92.9 92.7 93.5 93.493.9 93.7 8 92.9 92.7 93.5 93.3 88.5 88.1 9 92.7 92.4 93.7 93.5 94.294.0 10 93.1 92.9 No Data No Data 93.9 93.8 11 94.0 93.8 No Data No Data95.5 95.3 12 No Data No Data No Data No Data No Data No Data 13 No DataNo Data No Data No Data No Data No Data 14 93.7 93.4 No Data No Data95.4 95.2 15 94.0 93.7 No Data No Data 95.4 95.2

It will be readily appreciated by those skilled in the art thatmodifications may be made to the invention without departing from theconcepts disclosed in the foregoing description. Accordingly, theparticular embodiments described in detail herein are illustrative onlyand are not limiting to the scope of the invention, which is to be giventhe full breadth of the appended claims and any and all equivalentsthereof.

1. A reflective article, comprising: a substrate having a first majorsurface and a second major surface; a primary reflective coatingcomprising at least one metallic layer over at least a portion of amajor surface of the substrate; and a sacrificial anode in electricalcontact with the metallic layer of the primary reflective coating. 2.The reflective article of claim 1, wherein the metallic layer comprisesat least one metal selected from a group consisting of platinum,iridium, osmium, palladium, aluminum, gold, copper, silver, orcombinations or alloys thereof.
 3. The reflective article of claim 1,wherein the metallic layer comprises silver.
 4. The reflective articleof claim 1, wherein the sacrificial anode comprises a material having agreater oxidation potential than the metallic layer.
 5. The reflectivearticle of claim 1, wherein the metallic layer comprises silver and theanode comprises a material selected from the group consisting of copper,zinc, and magnesium.
 6. The reflective article of claim 1, wherein thesacrificial anode comprises an encapsulation structure comprising atleast one material having an oxidation potential operator than that ofthe metallic layer.
 7. A reflective article, comprising: a substratehaving a first major surface and a second major surface; a primaryreflective coating comprising at least one metallic layer over at leasta portion of a major surface of the substrate; and a source of electronsconnected to the at least one metallic layer.
 8. The reflective articleof claim 7, further including an anode connected to the source ofelectrons.
 9. The reflective article of claim 8, wherein the source ofelectrons comprises a source of electrical potential having a negativeterminal in contact with the metallic layer and a positive terminal incontact with the anode.
 10. The reflective article of claim 9, whereinthe source of electrical potential includes a photovoltaic array. 11.The reflective article of claim 9, wherein the source of electricalpotential includes a battery.
 12. The reflective article of claim 9,wherein the source of electrical potential comprises: a solar panelconnected to the metallic layer and the anode; and a battery connectedto the solar panel, the metallic layer, and the anode.
 13. A reflectivearticle, comprising: a transparent substrate having a first majorsurface and a second major surface; a base coat over at least a portionof the second major surface; a primary reflective coating comprising atleast one metallic layer over at least a portion of the base coat; atleast one solar cell; and an anode, wherein the solar cell iselectrically connected to the metallic layer and the anode.
 14. Thereflective article of claim 13, wherein the base coat comprises at leastone metal oxide selected from the group consisting of alumina, titania,zirconia, zinc oxide, zinc stannate, tin oxide, or combinations thereof.15. The reflective article of claim 13, wherein the metallic layercomprises at least one metal selected from a group consisting ofplatinum, iridium, osmium, palladium, aluminum, gold, copper, silver, orcombinations or alloys thereof.
 16. The reflective article of claim 13,including a protective coating over at least a portion of the primaryreflective coating, the protective coating comprising an inorganicmaterial selected from the group consisting of silica, alumina, or amixture thereof.
 17. The reflective article of claim 16, including anencapsulation structure formed over at least a portion of the protectivecoating.
 18. The reflective article of claim 17, wherein theencapsulation structure comprises a polymeric material or a ceramicenamel.
 19. The reflective article of claim 13, wherein the anodecomprises at least one of copper, magnesium, and zinc.
 20. Thereflective article of claim 13, further comprising a battery connectedto the solar cell, the metallic layer, and the anode.